This invention relates to deflection circuits for television receivers, for example.
Many regulated power supplies for television receivers provide AC line mains isolation by developing the supply voltages for the television receiver circuits from the voltages developed across windings of the horizontal output or flyback transformer. In these systems all the required power flows through the windings, with the power transfer synchronized with horizontal deflection. The unregulated voltage source is coupled to the flyback transformer primary winding. The regulated quantity is usually either the B+ supply voltage or the horizontal retrace pulse amplitude.
Horizontal deflection circuits typically operate in a resonant oscillatory mode. During trace, an approximately half-wave oscillation occurs between a horizontal deflection winding and an "S" shaping trace capacitor, and during retrace a half-wave oscillation occurs between the deflection winding and retrace capacitor. Also, during retrace a winding of the flyback transformer is coupled across the retrace capacitor to compensate for the power losses in the horizontal deflection circuit. Thus the flyback transformer is part of the horizontal retrace circuit. Any power or load variations at the flyback transformer influences the horizontal retrace time and results in picture width variations. Further, all the voltages derived from trace rectification, not just the voltage coupled to the varying load, vary at the same time. Loading of one trace rectified voltage terminal affects all the trace rectified voltages.
Loading of the flyback transformer also changes the duty cycle and consequently also the secondary voltages because the control circuit of the power supply typically affects either the retrace or trace voltage amplitude but not both simultaneously. Modulating the east-west raster correction by the sum of all load variations in order to obtain a constant, undisturbed picture as described in U.S. Pat. No. 4,129,806 by P. E. Haferl, may not be a complete solution because the trace derived secondary voltages of the flyback transformer are not compensated. Large load variations, caused by operation of a 10 watt audio amplifier circuit, for example, can no longer be compensated by the east-west raster correction circuit.